Transformer or choke



Sept. 25, 1934. c sNELL 1,974,588

TRANSFORMER OR CHOKE Filed March '7, 1932 2 Sheets-Sheet l Inverfi'S/ James C. Snell 27 MQAZAQ Sept. 25, 1934. J. c. SNELL TRANSFORMER OR CHOKE 2 Sheets-Sheet 2 Filed March 7, 193g InvernE/ James 0. mil i/mma I flfi'otfigys Patented Sept. 25, 1934 UNITED STATES PATENT OFFICE TRANSFORMER R CHOKE Application March 7, 1932, Serial No. 597,152

20 Claims.

This invention relates generally to transformers, chokes or the like, and particularly to improvements in transformers of the type used with radio loud-speakers.

One object of the invention is to provide a radio speaker transformer of new and improved character, capable of being made in small sizes and having a high efiiciency.

Another object of the invention is to provide a transformer of advantageous construction resulting in a compact and neat appearance and adapted for economical manufacture.

A further object of the invention is to provide a transformer or choke embodying an improved casing structure combined with an effectual sealing means for protecting the coil against moisture.

Yet another object of the invention is to provide a transformer for radio loud speakers having a protecting casing and a terminal plug combined therewith so as to facilitate electrical connection of the speaker to the radio.

Various improvements in construction and arrangment facilitating the assembly and production of the transformer also constitute objects of the invention as will become apparent from the following detailed description taken in connection with the accompanying drawings in which:

Figure 1 is a perspective view of a preferred form of transformer embodying the features of the invention.

Fig. 2 is a side elevational view of the transformer of Fig. 1 with the casing broken away'and the coil partially in section.

Fig. 3 is a vertical sectional view taken on line 33 of Fig. 2. The sealing compound, which for purposes of clarity has been omitted from the other figures, is here shown.

Fig. 4 is a fragmentary perspective view.

Fig. 5 is a perspective view, with the casing partially broken away, of a modified form of construction.

Fig. 6 is a perspective view of the transformer of Figs. 1 and 5 having a terminal plug integral therewith. The socket for the plug is shown in position for attachment. v

Fig. 7 is a side elevational view of another modifled construction.

Fig. 8 is a perspective view of the transformer of Fig. '7, partially broken away. 50 Fig. 9 is a slightly enlarged fragmentary detail taken on line 9-9 of Fig. 7.

For purposes of illustration, the invention is herein shown embodied in a transformer having a substantiallyrectangular shell-type core 10, one portion of which is formed by the usual E- shaped laminations (see Fig. 2) having parallel outer legs 11 and a central or intermediate leg 12. The other portion is formed by I-shaped laminations extending between the outer margins of the outer legs 11 to complete the magnetic circuits of the core. In the building up of the core 10, the laminations are not alternately assembled to form an overlapping joint, but each portion of the core is composed entirely of one form of lamination and the portions so resulting are preferably slightly spaced to provide gaps 13 in the magnetic circuits of the core. The length of the gaps is determined and maintained uniform by the insertion of a strip of non-magnetic material such as a sheet of paper 14; between the E- and 7 the I-portions of the core.

Mounted on the central leg 12 of the core is a coil 15, more particularly described and claimed in my copending application Serial No. 597,153, filed March 7, 1932, containing a primary winding 7 15 and a secondary winding 15 insulated from each other by a circumferential strip 15 and from the core by binding strips 15 of suitable insulating material. The ends of each of the windings are brought out on the same side of the coil 15 and terminate in leads 16. By a unique construction of the coil wherein the windings are solidly wound, that is, composed entirely of turns of wire in bodily contact and not separated into layers by strips of paper or the like, which windings are coextensive with the core of the coil and securely retained by binding strips wrapped around the windings, the coil 15 is made unusually small and compact, thereby requiring but comparatively little space between the central leg 12 and the outer legs 11, and permitting the use of a core materially smaller in overall dimensions. The coil 15, because of its construction, also projects beyond the sides of the core 10 but a comparatively small distance.

Means is provided for retaining the portions of the core 10 in proper spaced relation. Herein this means is in the nature of a casing adapted to receive the core 10 and the coil 15 snugly within it, forming thereby a protecting means for the coil 15 as well as a retaining means for the portions of the core 10. The casing comprises generally a shell 1'7 providing three edge walls of the casing, plates 18 constituting the sides of the easing, and a channel-shaped cap 19 forming the remaining edge wall and completing the casing.

The shell 17 is preferably metallic and generally U-shaped, having an intermediate portion 20 forming one end edge wall of the casing and perpendicular side portions 21 forming the opposite I 10 legs 11 thereof.

side edge walls thereof. The intermediate and side portions 20 and 21 are so proportioned that the shell is adapted to receive the core snugly and thus firmly retain it in position while maintaining the proper gap in the magnetic circuit.

An interengaging relation is employed between the shell 17 and the side plates 18so'as to retain the latter firmly in position; To this end the edges of theportions 20 and 21 are herein bent inwardly to form peripheral flanges 22. The channel shape so given to the portions 20 and 21, which are substantially greater in width than the thickness of the core 10, adapts the shell 1'7 slidably to receive the side plates 18 through its open edge, thereby securely retaining the plates against removal by pressure applied from within the casing. The ends of the portions 21 are bent at right angles to form ears 23 apertured to receive rivets 24 by means of which the cap 19 is attached to the shell.

In the preferred construction illustrated in Figs. 1 to'4, the side plates 18 are metallic and each formed with an outwardly bulging central portion 25 which receive the laterally proiecting portions of the coil 15. The upper and lower edges of the side plates 18 (see Fig. 3) are bent inwardly to form flanges 26 which, in the assembled transformer, bear along the outer legs 11 of the core and the ends of the I-shaped laminations. The flanges 26 thus bearing against the core 10 retain the laminations closely assembled and space the side plates 18 and the peripheral flanges 22 from the core. Any suitable number of apertures are formed in the side plates 18 through which the leads 16 from the coil 15 project.

To facilitate assembly of the transformer and to obtain other advantages, presently to be pointe'd out, the flanges 26 are bent beyond the normal to the plane of the plates 18 and formed with a rounded outer edge 2'1. The rounded edges 27 so formed insure that the upper end of the plates 18 will slide easily beneath the portions of the peripheral flanges 22 on the end edge 20.v

The oblique position of the flanges 26 also gives to them a degree of resiliency which permits them to yield in the assembly of the transformer and insures that the laminations are firmly compressed to prevent chattering. With the flanges 26 bearing on the core 10 inwardly of the line of contact between the plates 18 and the peripheral flanges 22, the compressive force applied as a result of the insertion of the plates in the channelshaped end portion 20 tends to how the plates outwardly into tight engagement with the flanges 22 of the side edges 21.

Assembly of the transformer as described is as follows: The coil 15 is first mounted on-the central leg 12 of the E-shaped portion of the core 10. Plates 18 are then placed on the sides of the core with the flanges 26 hearing along the outer The non-magnetic strip 14 is next placed over the ends of the legs of the core and is there retained in position by the flanges 26 while the I-shaped laminations are assembled. With the I- and the E portions of the core now held in position by the side plates 18, the core and the plates are inserted into the shell 17 through the open edge thereof, preferably with the legs of the core parallel with the end edge 20. In the preferred mode of construction, a sealing compound is then introduced into the casing in a manner to be presently described, and the cap 19 is then riveted to' the shell 17 to complete the assembly.

' The transformer thus constructed is admirably The actual size of the openings will vary with the size and shape of the nozzle of the means employed in injecting the compound. Herein an aperture 29 is formed in the lower flange 26 of each of the side plates 18 which apertures are thus concealed by the cap 19. Injecting the compound under pressure materially speeds up the manufacturing process.

The metallic side plates 18 of the preferred construction are also especially adapted for the support of a terminal plug 30 facilitating the connection of the speaker, with which the transformer is employed, to the radio set. It is the general commercial practice at this time for the manufacturer of the speaker to supply the speaker to the trade with the leads from the fleld and voice coils of the speaker, and the leads from the primary of the transformer attached to a terminal plug, such as the plug 30. This plug is customarily attached at the ends of leads varying in length from 18 to 24 inches and is so mounted because of the lack of means whereon the plug ward small sets, the space required by the socket.

itself and to make the socket accessible is very valuable but the provision of the space cannot, under present constructions, be avoided. Another disadvantage in the attachment of the plug at' the end of long leads is the frequent rupturing of the diaphragm of the speaker by an accidental striking thereof by the plug These disadvantages can all be avoided and many new advantages obtained by a mounting of the plug 30 directly on the transformer, first made possible by the construction of the transformer as herein disclosed. The plug 30 may have any proper number of prongs 31. Herein four prongs 31 are shown secured to a base plate 32 of insulating material which is conveniently attached to the side plate 18 by insertion beneath flanges'33 struck out of the side plate. The side plate 18 is cut away back of the base plate 32 to permit connection of the primary winding and to prevent contact between the inner ends of the prongs 31 and the side plate. The base plate 32 thus forms a part of the casing. Two of the prongs 31 also have at their base auxiliary contacts 34 to facilitate the attachment of the leads from the field coil of the speaker.

With the plug 30 thus mounted directly on the transformer the necessity for special leads from the primary winding is avoided and the winding may be connected to the plug 30, without danger of breaking, by the fine wire comprising the winding. The danger of puncturing the diaphragm of the speaker is also avoided.

The socket which was formerly mounted within the chassis of the radio is, in the present construction, removed therefrom and shown at 35 attached to the end of leads 35 projecting through an aperture in the chassis of the radio (not shown). The socket 35 is formed with a skirt 36 which, when connection is made to the plug 30, projects over all contacts to leave no exposed wires from which a shock might be obtained. One or more apertures 37 may be formed in the skirt 36 through which the leads attached to the auxiliary contacts 34 are received. The arrangement of the plug 30 and socket 35 thus eliminate all the disadvantages present in the former construction and provide new advantages in a construction of no substantially increased cost.

Maximum efficiency and proper operation of the transformer is obtained by a determination and maintenance of the correct gap in the magnetic circuits of the core 10. In order that the effectiveness of the gap be not destroyed, a bridging thereof by adjacent magnetic material must be avoided, To this end means is provided to space the end edge portion 20 of the shell and the cap 19, which would otherwise form such a bridge, from the core. In the preferred construction, such spacing is effected by means of sharp edged ribs 38 formed in the intermediate portion 20 of the shell 17 and the cap 19 so as to provide sharp inner edges extending transversely thereof. Two ribs are, herein, formed in the portion 20 and the cap 19 with each rib spaced, approximately a distance equal to one-half the width of the I-shaped lamination, from the side portions 21. Such spacing insures that one of the ribs 38 will always bear against the I-shaped portion and the other against the E-shaped portion even if the position of the core is reversed from that shown in Fig. 2. The shell 17 and the cap 19, while thus effective to retain the core and individual laminations in position, do not effectually bridge the gap because of the small area of contact provided by the ribs.

The side plates 18, which if bearing bluntly against the outer legs 11 of the core would also bridge the gap, are prevented from so doing by the flanges 26 which space the plates 18 from the core. The flanges 26 are rendered ineffectual to bridge the gap because of their knife edge contact with the core obtained as a result of the oblique position of the flanges.

In the modified construction disclosed in Fig. 5, the flanges 26 are replaced by fibre-spacing means in the form of washers 39 which are made from any suitable resilient material such as fibre or rubber and conform to the shape of the core. The washers 39 are porous and have a degree of resiliency which permits them to be compressed before insertion into the shell 17 so that after insertionthey may expand and retain the core 10 firmly in position and prevent chattering thereof. The washers 39, being of rubber or other resilient material and therefore nonmagnetic, also serve to prevent a bridging of the gaps in the core 10 by the metallic side plates 18. To protect the coil 15 from moisture the washers 39 may be impregnated with a sealing compound which then form with the core and side plates a sealed chamber about the coil.

Figs. 7 to 9 disclose another modified construction. In this modification, the shell 17 is made of a depth such that the side plates 18 require no bulge to accommodate the lateral projections of the coil 15. Herein, the plates 18 are flat pieces of composition such as a resinous condensation product. The non-conducting side plates so formed are well adapted to carry terminals 40 permitting the direct attachment thereto of the windings of the coil 15 without the provision of special leads. To protect the coil 15 from moisture and to space the core and retain the lamination thereof tightly compressed to avoid chattering, the casing is filled with a sealing compound 41.

Another feature of the modification disclosed in Figs. 7 to 9 is the provision of a non-magnetic, metallic clip 42 of brass or the like which is adapted to fit over the outer legs 11 of the core. The clip 42 is made approximately as long as the dimension of the core parallel to the outer legs 11 and thus extends over the gaps formed in those legs. In the assembly of the transformer, the clip 42 is mounted on the E-portion of the core and thus forms a retaining means in which the I-shaped-laminations are assembled and in which they are held while the core is inserted into the shell 17. The clip 42 serves another purpose in that it spaces the core from the cap 19 and the portion 20 of the shell 17 to prevent a bridging of the gap thereby. The formation of spacing ribs in those portions of the shell adjacent the gaps is thus obviated.

I claim as my invention:

1. In a transformer or choke having a fiat, shell-type core, a casing comprising a shell having inturned edges, side plates closing the open faces of said shell and retained against lateral removal by said inturned edges, said plates being slidably received in said shell with said core therebetween, a cap for retaining said plates and said core within said shell, and spacing means between said side plates and core.

2. In a transformer or choke having a flat shell-type core, a casing comprising a shell forming edge walls of the casing and having inturned edges, plates forming the side walls of the casing and with said core therebetween slidably received within said shell and retained against lateral displacement by said inturned edges, resilient, inwardly projecting flanges on the edges of said plates bearing against the core to compress the laminations thereof, and a cap secured to said shell and completing said casing.

3. In a transformer or choke having a shelltype core with a central and outer legs, gaps in the legs and windings on the central leg of the core, a casing comprising a shell forming edge walls of the casing and having inturned peripheral flanges, plates forming the side walls of the casing and with the core therebetween slidably received in said shell between said flanges, inwardly projecting flanges on said plates bearing with knife-edge contact along the outer legs of the core, and a cap secured to said shell to retain the core and said plates within said shell.

4. A transformer or choke comprising, in combination, a core composed of E- and I-shaped laminations assembled to form separable portions, a sheet of non-magnetic material interposed between the portions of the core to form gaps in the magnetic circuits thereof, windings on the central leg of said core, a U-shaped shell adapted to receive the core snugly within, a cap secured to said shell to retain the laminations of the core firmly in position, and means reducing the magnetic bridging effect of said shell and said cap across the gaps.

5. A transformer or choke comprising. in combination. a core composed of E and I-shaped laminations assembled to form separable portions, means spacing the portions of the core to form gaps in the magnetic circuits thereof, windings on the central leg of said core, a metallic shell adapted to receive the core snugly within, said core being inserted with the I-portion parallel with the side edges of the shell, an end cap retaining said core in said shell, and ribs formed in said cap and the end edge of said shell and bearing against the portions of said core to space said shell and said cap from said core.

6. A transformer or choke comprising, in combination, a core composed of E- and I-shaped laminations assembled to form separable portions, a sheet of non-magnetic material interposed between the portions of the core to form gaps therebetween, windings on the central leg of said core, and a casing for said core and windings comprising a shell, plates forming the sides of the casing and received slidably within said shell with said core therebetween, an end cap retaining said core and plates snugly in said shell, flanges on said plates bearing with knife-edge contact on the outer legs of said core, and means in said cap and shell spacing the same from the portion of the core containing the gaps.

7. A transformer comprising, in combination, a core composed of E- and I-shaped laminations assembled to form separable portions, said portions being spaced to form gaps in the magnetic circuits of the core, windings on the central leg of said core, a shell having channel-shaped portions, side plates fitting over the faces of said core and windings and with said core slidably received within the channel-shaped portions of said shell, a cap secured to said shell to retain said core and said plates therein, and spacers of non-magnetic material interposed between said plates and said core, and means formed in said cap and shell in the portions adjacent the gaps to reduce the bridging effect across the gap of said shell and side plates.

8. A transformer or choke comprising, in combination, a core having a gap in the magnetic circuit, a metallic shell forming a retainer for said core, said core fitting snugly within said shell to have its parts thereby retained in position, and a clip of non-magnetic material on said core over said gap.

9. A transformer or choke comprising, in combination, a core composed of E- and I-shaped laminations assembled to form separable portions, said portions being spaced to form gaps in the magnetic circuits of the core, windings on the central leg of said core, a metallic shell adapted to receive the core snugly within to form a retainer therefor, and a clip of non-magnetic material on the outer legs of said core to maintain said I-shaped laminations in position and to space the gap in the outer legs from said shell.

10. A transformer or choke comprising, in combination, a core composed of E- and I-shaped laminations assembled to form separable portions, non-magnetic clips on the outer legs of the portion formed by said E-shaped laminations receiving the ends of the I-shaped laminations, a shell having inturned edges and adapted to re- 'ceive said core within, plain side plates slidably received in said shell at each-side of said core and retained by said inturned edges, and a sealing compound in the casing formed by said shell and side plates to retain said core in position.

11. A transformer or choke comprising, in combination, a core composed of E- and I-shaped laminations assembled to form separable portions, windings on the central leg of said core, a shell having inturned edges and receiving said core within, side plates of non-conducting material slidably received in said bracket between said core and said inturned edges, terminals on said side plates connected to the ends of said windings, and a sealing compound filling the spaces in the casing formed by said shell and side plates.

12. A transformer or choke comprising a core, windings on said core, and a casing enclosing said core and windings comprising side plates positioned on opposite sides of said core, flanges on said plates spacing the plates from said core,

a shell adapted to receive said plates and core slidably within, and a cap securing said plates and core within said shell, said flanges having apertures concealed by said cap adapted for the injection of sealing compound into the casing.

13. A transformer or choke comprising, in combination, a shell-type core, a primary and secondary winding on said core, a casing for said core and windings comprising a shell adapted to receive said core snugly within it and side plates having an interengaging relation with said shell to be thereby secured on opposite sides of said core, one of said plates having an aperture giving access to the ends of the primary winding, and a terminal plug mounted on said side plate over the aperture and connected with the primary winding.

14. In a speaker transformer having a core and windings and adapted to be employed with a speaker having a field coil, a casing for the core and windings comprising rigid side plates adapted to be positioned on opposite sides of said core, one of said plates having an aperture, and a shell adapted to receive said core and windings, and a terminal plug having a base mounted on said apertured side plate to close the aperture therein, and prongs projecting from said base and adapted to be connected with a winding of the transformer and the field coil of the speaker.

15. A transformer or choke comprising a shelltype core having a central leg, outer legs and connecting portions, a winding on said central leg and circumscribed by said outer legs and connecting portions, and a casing constituting a retainer for said core and winding, said casing comprising a U-shaped shell having inturned edges forming channels, plates placed over the opposite faces of said core and slidably received therewith in said shell through the open side thereof, and an inwardly projecting resilient flange on the sides of said plates parallel with the open side of said shell bearing against a portion of the core circumscribing said winding whereby said core is tightly gripped in said shell and said winding is efiectively enclosed.

16. A transformer or choke comprising a shelltype, substantially rectangular core, a winding on said core, and a casing constituting a retainer for said core and winding comprising a U-shaped shell having its edges turned inwardly to form channels, plates placed over opposite faces of said core and therewith slidably received in said shell through the open side thereof, and a flange along the exposed edge of the plates bearing against said core thereby effectively enclosing said winding, said flange having an aperture large enough to permit the insertion of sealing compound but not so large as to render the flange ineffective to retain the compound in the casing.

1'1. A transformer or choke comprising a shelltype, substantially rectangular core, a winding on said core, and a casing constituting a retainer for said core and winding, said casing comprising a U-shaped shell the edges of which are turned inwardly to form channels, plates adapted to be placed over the opposite faces of said core and slidably received therewith within said shell, and a rounded edge formed on that side of said plates which projects into the intermediate portion of said U-shaped shell to facilitate insertion beneath the inturned edges of said shell.

18. A transformer or choke comprising a shelltype, substantially rectangular core, a winding on said core, and a casing constituting a retainer for said core and winding, said casing comprising a U-shaped shell the edges of which are turned inwardly to form channels, plates adapted to be placed over the opposite faces of said core and slidably received therewith within said shell, and flanges on the edges of the plates parallel with the open side of said shell bent inwardly beyond a perpendicular to the plates to render them slightly yieldable and to form a rounded edge facilitating insertion of the core and plates into said shell.

19. In a transformer or choke having a flat,

shell-type core, a casing comprising a U-shaped shell formed of channel-shaped portions, side plates positioned on opposite sides of the core and slidably received therewith in the channelshaped portions of said shell, and resilient spacing means interposed between said plates and said core to compensate for slight variations in the dimensions of the core or shell.

20. In a speaker transformer having a core and a primary and a secondary winding, a casing for the core and windings completely enclosing the windings, said casing having an aperture giving access to the ends of the windings, and a plural contact terminal 'plug mounted on said casing over the aperture and connected with at least one of the windings.

JAMES C. SNELL. 

